Add a delay when TERMinating a process

Otherwise we might end up missing the signal and fail later when
reset the process.  All tests are passing in OSX now.

bin/varnishtest/vtc_process.c

@@ -756,6 +756,7 @@ cmd_process(CMD_ARGS)
 		}
 		if (!strcmp(*av, "-stop")) {
 			process_kill(p, "TERM");
+			sleep(1);
 			continue;
 		}
 		if (!strcmp(*av, "-wait")) {